Motion quality is a contributor to image quality (IQ) problems in printers and copiers and may occur as the printing system degrades due to ordinary wear-and-tear, contamination and/or a failure in one of its parts. Motion quality errors may occur due to uncontrolled speed or velocity changes of parts in the printer, such as intermediate belts and photoreceptor surfaces. Examples of motion quality errors seen on output prints include distorted images in the process direction, improper alignment of content in the process direction, offset lines of text, improper line spacing, improper character spacing, etc.
It is known to detect IQ defects before they become a problem by monitoring the motion quality of a marking engine. For example, test targets, such as “ladder charts,” have been used, and are very accurate for this purpose. However, printing test-targets interrupts regular print jobs and wastes valuable resources.
Methods are also known which detect bands and streaks using printed documents themselves. These methods rely primarily on pictorial and/or color portions of the images to determine many uniformity-based IQ defects such as, for example, bands, streaks, mottle and graininess.
However, portions of the printed images that contain text features are generally not considered for further analysis because they are not believed to provide much useful information for IQ analysis.